From Yotam Ottolenghi in The Guardian. Though I think he may have been kidnapped by aliens and replaced, 1 celeriac seems a bit imprecise. Delicious though. You could make it GF if you used gram flour.

Combine the celeriac, potato, shallot and lemon juice in a medium bowl with two teaspoons of salt, then tip into a sieve lined with a clean tea towel or cheesecloth. Set the sieve over a bowl and leave for 30 minutes, for the liquid to drain off. Draw together the edges of the towel, then wring it a few times, to get rid of as much water as possible. Transfer to a clean bowl and combine with the spices, garlic, eggs and flour. Using your hands, form the mix into 10 6cm-wide patties, compressing the rösti as you make them, to squeeze out any remaining liquid.

Put all the salsa ingredients in a separate bowl, add a generous grind of pepper and mix to combine.

Pour enough oil into a medium-sized nonstick frying pan to come 1.5cm up the sides. Put the pan on a medium heat and, once the oil is very hot, fry the rösti in batches for seven minutes, turning them a few times, until crisp and golden-brown all over. Transfer to a plate lined with kitchen towel and keep warm while you cook the rest of the rösti. Serve at once with the salsa and a spoonful of soured cream.